This invention relates to a device for detecting the rotation of a steering wheel for motor vehicles in which an information representative of the rotation of the steering wheel is outputted as electrical signals.
Recently, in order to achieve a better steering stability and a more comfortable ride in motor vehicles, it has been considered to control a damping force of a suspension, to control a gear shift position of an automatic transmission, and to control the steering of rear wheels (in case of a so-called four wheel drive steering system) in accordance with the angle of rotation of the steering wheel or steering angle in accordance with the angle of rotation of the steering wheel or steering angle and the running speed.
Conventionally, as one example of steering wheel rotation-detecting devices used for such controls, there has been provided an optical-type device having an encoding member comprising a disc which is rotatable with a steering shaft and has a plurality of through holes serving as markers in such a manner that the through holes are arranged in an annular form so as to be concentric with respect to the center of rotation of the disc, and two pairs of transmission-type photo-interrupters serving as sensors are disposed in such a manner as to correspond to the above array of through holes so that two kinds of pulse signals having different phases are obtained based on outputs of these photo-interrupters. In this case, the direction of rotation of the steering wheel can be detected based on the phase difference between the above two kinds of pulse signals, and also the amount of rotation of the steering wheel can be detected based on the number of these pulse signals. Conventionally, the encoding member is housed and held in a first casing, and the photo-interrupters as well as a signal generating circuit for producing the pulse signals based on the outputs of the photo-interrupters are housed and held in a second casing separate from the first casing. When the steering wheel rotation-detecting device is to be assembled, the first casing is first attached at a predetermined position, and then the second casing is attached relative to the first casing.
With the above construction having the separate first and second casings, the relative position between the encoding member and the photo-interrupters may be changed when an external force is applied to one of the casings at the time of the assembling, repair, inspection, etc., in which case it is sometimes impossible to obtain the pulse signals.